DirectX is a windows API for drawing sophisticated graphics on windows computers.
It sits between the the developer writing his (typically a game) and your graphics card and driver.
As graphics cards improve the DX library becomes out of date as it won't have functions for the new stuff on the market. Graphics card manufacturers know that no-one will buy there new cards if the latest games don't support the latest effects, so there's a massive marketing collusion going on to create hype over the whole thing, so that we all feel compelled to upgrade our graphics cards every 6 months, because games are soooo complicated these days you can't get past the first level anymore, but at least you can marvel at the life like reflection of your doomed pilot in the cockpit glass as you auger into the ground.
(you might detect a note of cynicism in my post, just in case you're wondering it is deliberate)